The number of people in the world relying on manual wheelchairs for primary mobility has grown significantly in the past few decades and is approximated to be near 1.5 million in the United States alone. Secondary injuries such as carpal tunnel syndrome (CTS) are prevalent in manual wheelchair users (MWUs) with some studies finding up to 63% prevalence (Aljure, et al, "Carpel Tunnel Syndrome in Paraplegic Patients" Paraplegia 23; International Medical Society of Paraplegia (1985). Nonetheless, MWUs must use their arms in almost every daily activity and the option of a power wheelchair to prevent overuse injuries is often not economically feasible and undesirable for other reasons. Although there are several CTS-preventative propulsion devices commercially available (e.g., add-on lever crank devices), the high prevalence of injury remains. Further, the best clinical solution to relieve some of the injuries leave individuals unable to self-propel for extended periods of time. For example, the best resolution to CTS, carpal tunnel release surgery, often leaves an individual unable to self-propel or work for weeks and some times months. Thus, because of the limited options available, most MWUs ignore pain and trauma to their hands and arms during propulsion and continue the everyday activities, regardless of the risk of long-term harm. These phenomena have prompted research establishing a nexus between wheelchair propulsion biomechanics and highly prevalent secondary injuries.
In studies investigating secondary upper extremity injuries, the high prevalence of injuries has been attributed to over use of the arms during daily wheelchair propulsion. Many researchers believe the inefficient transmission of power from the hand to the pushrim is the phenomena predominantly responsible for nerve dysfunction in the upper extremities. For example, recent studies on wheelchair propulsion biomechanics relate CTS in MWUs to higher propulsion forces applied to the pushrim and to greater stroke frequency during wheelchair propulsion (Baldwin et al "A Relationship between Pushrim Kinetics and Median Nerve Dysfunction). Several studies on CTS in the able-bodied working population have found that long term exposure to high repetitious forces to the hand and wrist can cause CTS (Silverstein et al, "Occupational Factors and Carpal Tunnel Syndrome" American Journal of Industrial Medicine; Vol. 11 (1987)).
Current commercially available wheelchair pushrims, 10, are typically made of aluminum tubing with a tube diameter, 11, of 3/4", a 21" overall rim diameter, 12, and typically positioned 1/2" or 5/8" away from the wheel, 13, as shown in FIGS. 1a and 1b. A high friction vinyl coated pushrim also exists that has dimensions similar to those of the standard rims.
Unfortunately, the tube diameter, 11, of standard pushrims is too small to allow complete grip between the palm of the hand and the fingers. This creates a number of problems. First, it reduces the contact area between the hand and the pushrim, which increases the pressure on the contact points of the hand, and increases the forces transmitted to the delicate structures of the hand. Second, the inability to grip the pushrim with the entire palm and fingers reduces the mechanical efficiency by recruiting muscles for stabilization on the rim instead of delivering power to the wheelchair. Thus, the decreased mechanical efficiency and increased forces while using standard pushrims may contribute to developing secondary injuries like CTS.
Accordingly, it is an object of the present invention to provide a pushrim that reduces higher pushrim forces. It is a further object of this invention to decrease the propulsion frequency. It is another object of this invention to increase the mechanical efficiency of a pushrim by providing a better fit to the hand. It is also an object of this invention to decrease the likelihood that an individual will develop injuries including CTS.